The present invention relates to the texture of polycrystalline materials and further relates to methods of determining or quantifying the texture homogeneity of polycrystalline materials. The present invention further relates to sputtering targets and determining sputtering efficiencies in sputtering targets.
Certain properties of polycrystalline materials, including deformation behavior, magnetic permeability, corrosion rate, and resistance to electromigration are generally dependent on the arrangement of atoms within the material (J. A. Szpunar, Texture Design for New Application, Proceeding of the Twelfth International Conference on Textures of Materials, J. A. Szpunar (ed.), NRC Research Press, Ottawa, pp. 6, 1999), incorporated in its entirety herein by reference. Often, the processes utilized to manufacture wrought metals and alloys impart a preferred orientation to the individual crystallites in the material. Crystallographic texture refers to the alignment of atomic planes within a material, and the Orientation Distribution Function (ODF) provides a mathematical description of the arrangement of all crystallites with respect to a specific coordinate system, such as the rolling direction, transverse direction, and normal direction of a rolled plate (H. J. Bunge, Introduction to Quantitative Texture Analysis, Advance and Applications of Quantitative Texture Analysis, H. J. Bunge and C. Esling (eds.) DGM Informationsgesellschaft mbH, Oberursel, Germany, pp. 3-18, 1991; H. J. Bunge, Representation and Interpretation of Orientation Distribution Functions, Advances and Application of Quantitative Texture Analysis, H. J. Bunge and C. Esling (eds.) DGM Informationsgesellschaft mbH, Oberursel, Germany, pp. 19-48, 1991), both incorporated in their entirety herein by reference.
Conventionally, diffraction techniques are used for determining the preferred orientation of materials. These methods generate pole figures, a 2-dimensional representation of the distribution of a normal (i.e. pole) of a specific atomic plane about the measurement surface of the sample. A 3-dimensional description of the texture can then be calculated by mathematical inversion of several different pole figures (H.-J. Bunge, Texture Analysis in Materials Science, Cuvillier Verlag, Gxc3x6ttingen, Germany, pp. 2-118, 1993), incorporated in its entirety herein by reference. X-ray and neutron diffraction are considered integrative measurement techniques. These methods require that a relatively large area of the sample be irradiated in order to collect bulk diffraction information for a statistically significant number of grains.
While conventional diffraction techniques can be used to adequately determine the bulk texture of materials, they are incapable of identifying the presence of texture inhomogeneities within the sample. The existence of discontinuous textures has been shown to significantly influence the performance of engineering materials. For example, secondary recrystallization and growth of (011) grains enhance the magnetic permeability of SiFe (H. J. Bunge, Industrial Applications of Texture Analysis, Advances and Application of Quantitative Texture Analysis, H. J. Bunge and C. Esling (eds.) DGM Informationsgesellschaft mbH, Oberursel, Germany, pp. 241-278, 1991), incorporated in its entirety herein by reference, and sharp bands of localized textures impact the deformation and sputtering performance of tantalum (S. I. Wright, G. T. Gray, and A. D. Rollett, Textural and Microstructural Gradient Effects on the Mechanical Behavior of a Tantalum Plate, Metallurgical and Material, Transactions A, 25A, pp.1025-1031, 1994; C. A. Michaluk, D. B. Smathers, and D. P. Field, Affect of Localized Texture on the Sputtering Performance of Tantalum, Proceedings of the Twelfth International Conference on Textures of Materials, J. A. Szpunar (ed.), NRC Research Press, Ottawa, pp. 1357-1362, 1999), all incorporated in their entirety herein by reference. An efficient and reliable means of revealing texture homogeneity is to use Orientation Imaging Microscopy (OIM). With OIM, the orientation of each individual crystallite can be determined by probing with an electron beam and then indexing the resultant Kikuchi pattern (B. L. Adams, D. L. Dingley, K. Kunze, and S. I. Wright, Orientation Imaging Microscopy: New Possibilities for Microstructural Investigations Using Automated BKD Analysis, Materials Science Forum, Vol. 157-162, pp.31-42, 1994; Advanced Materials Analysis Via Orientation Imaging Microscopy (OIM), TSL Technical Note, TexSEM Laboratories, Draper, UT), both incorporated in their entirety herein by reference. The global texture can then be roughly determined from discrete orientation data (S. Matthies and G. W. Vinel, On Some Methodical Developments Concerning Calculations Performed Directly in the Orientation Space, Materials Science Forum, Vol. 157-162, pp.1641-1646, 1994), incorporated in its entirety herein by reference.
Using OIM, the textural uniformity can be displayed in the form of an Inverse Pole Figure (IPF) map, which is a micrograph where each discrete grain is color-coded with respect to this crystal orientation. Textural gradients and bands are represented as respective color gradations and striations in the IPF map. However, visual interpretation of an IPF provides a very subjective description of the texture character of the samples. While a visual representation of the texture of polycrystalline materials is helpful in revealing any texture inhomogeneity in polycrystalline materials, an interpretation must be made and interpretations may significantly vary from person to person. Also, visual representations of texture can only provide a general idea as to texture homogeneity. Accordingly, there is a need in the analytical and industrial areas to somehow quantify texture homogeneity that exists in polycrystalline materials. Quantifying texture homogeneity will provide an objective determination and avoid varying subjective determinations. Thus, a standard unit can be created with respect to texture homogeneity that could be used by the analytical and industrial community in understanding the texture homogeneity existing in polycrystalline material. This would have commercial benefits, such as predicting the sputtering efficiency of targets as well as setting industry standards for the manufacturing of polycrystalline materials where texture homogeneity is one of the criteria of an acceptable product.
A feature of the present invention is to provide a method for quantifying texture homogeneity in polycrystalline material.
Another feature of the present invention is to provide methods to predict the sputtering reliability of sputtering targets.
A further feature of the present invention is to provide a method to create an objective determination of texture homogeneity for use as an industry standard.
An additional feature of the present invention is to provide a system to quantify texture homogeneity in polycrystalline material.
Additional features and advantages of the present invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the description and appended claims.
To achieve these and other advantages, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention relates to a method for quantifying the texture homogeneity of a polycrystalline material. The method involves selecting a reference pole orientation. Further, in this method, a cross-section of the polycrystalline material which has a certain thickness is scanned in increments through the thickness using scanning orientation imaging microscopy (OIM) to obtain crystal orientations of a multiplicity of grains that exist in the incremental thickness of the cross-section of the material. Methods other than OIM can be used to obtain the crystal orientations. The orientation differences between the reference pole orientation and the actual crystal orientation obtained for each grain through scanning can then be determined. A value of misorientation from the reference pole orientation at each grain measured throughout the thickness can then be assigned and then an average misorientation of each measured increment throughout the thickness of the cross-section of the material can be determined. Once determined, the severity of texture banding can be determined by taking a second derivative of the average misorientation of each measured increment through the thickness of the cross-section of the material. This second derivative represents the texture banding and provides a quantitative number as to the texture homogeneity of the polycrystalline material that has been tested. A number that is closer to zero represents a material that has good texture homogeneity (e.g., a material having very few inflection points with respect to the severity of banding).
The present invention also relates to a method to predict the sputtering reliability of a target that involves quantifying the texture homogeneity of the target by taking a cross-section of the target for sampling purposes and obtaining the texture banding of the sample. The texture measurement then provides a predictive value as to the sputtering efficiency of a target and a number close to zero represents a target that has consistent sputtering efficiency.
The present invention also relates to a system for quantifying the texture homogeneity of a polycrystalline material which includes a scanning orientation imaging microscope or other device that measures crystal orientations, such as x-ray micro-diffraction, and means to determine the average misorientation of each measured increment throughout the thickness of the material being tested and means to determine a texture homogeneity by taking the second derivative of the average misorientation of each measured increment through the thickness of the material being tested.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a further explanation of the present invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate several embodiments of the present invention and together with the description, serve to explain the principles of the present invention.
All patents and publications mentioned above and throughout the present application are incorporated herein in their entirety and form a part of the present application.